The disclosures herein relate generally to implants for prosthetic joints and more particularly to preparing cuts in bones for fitting such implants, such as preparing femoral cuts in the distal femur.
Preparing the distal femur to receive the femoral component of a knee prosthesis, involves several accurately located cuts in the bone surface of the femur. Typically, the first cut establishes a transverse surface and a second cut may establish a reference, anterior surface. This provides a locating surface for a cutting guide which is used to assist in accurately cutting the additional surfaces needed to locate and secure the implant of the femoral knee prosthesis.
One method used for preparing the additional cuts includes a combination of cutting guides commonly known as speed blocks, all-in-one blocks, and four-in-one blocks. These are cutting guides for supporting and guiding an orthopedic saw blade during the preparation of the distal femoral chamfered surfaces for the femoral component of the knee prosthesis. All chamfered and square cuts can be made with one instrument without removing the device so that the user is not forced to use an additional block or blocks with different cutting surfaces and angles to complete the cuts. Another method involves using independent chamfer blocks that only allow one, two, or more cuts. This involves removal of the first block from the bone and replacing it with a second block to complete the cuts.
One approach to this problem is disclosed in U.S. Pat. No. 4,892,093, which describes a cutting guide for guiding a saw blade during the preparation of a femur for the implant of the femoral component of the knee prosthesis. This device includes guide surfaces for enabling the cutting of the anterior femoral cut, the posterior femoral cut, the anterior chamfer cut, and the posterior chamfer cut, while the cutting guide remains located and secured to the femur in a single position on the transverse surface located along the distal femur.
Another approach is disclosed in U.S. Pat. No. 5,411,505, which describes a jig for resecting the distal end of a femur to receive the femoral component of the knee prosthesis. The jig has independent medial and lateral condyle sagittal saw guides. The guides aid the user in cutting three of four resected surfaces or planes for each condyle. The femoral component accepts shims over either condyle to compensate for uneven loss of healthy bone. Each saw guide slides on a slanted dovetail track so that the proper amount of anterior displacement can be maintained.
Presently known methods have their respective advantages and limitations. One limitation is that in one known method, the user is making blind cuts and has no accurate method for checking the flatness of each cut; a factor which can be critical for a bone-ingrowth device. Another limitation is that in another known method, the user has the advantage of being able to verify each cut with a flat, straight edge after each cut is made, for each cut surface. However, because this method requires that the blocks must be removed and replaced in the bone at least two times, error is more likely. Also, if the bone is soft, the locating holes for the blocks can become elongated, thus allowing the cutting surfaces to move when pressure from the saw blade is applied. This creates a burdensome requirement in the manufacture of these devices, because manufacturers are forced to supply both of the described types of cutting blocks on either a production and/or custom basis to satisfy customer demand.
Therefore, what is needed is a device and method which gives the user the advantages of both of the above types of chamfer blocks without the limitations of each, and which permits the manufacturers to avoid the expense of producing two different devices that perform the same function.